For the backend, Kotlin on Intellij. It's crazy awesome and you can use it now for android clients as well. The Javascript transpiler is probably not ready yet

For the backend, Kotlin on Intellij. It's crazy awesome and you can use it now for android clients as well. The Javascript transpiler is probably not ready yet (in beta) so I would use a Bootstrap and/or Material Design library with lots of components and tie it together with javascript. Database Postgres. You can go hard relational if that's appropriate or use the Json support like a better Mongo.